Relaxation and shear viscosity in mixed ionic melts

A linear dependence was found between the reorientational linewidth for alkali nitrate melts, obtained by Raman measurements, and the ratio of temperature divided by shear viscosity. An interpretation of this result in the framework of the Stokes-Einstein-Debye (SED) model leads to a volume for the ${\mathrm{NO}}_3$ anion which is very close to a literature value. Using this volume, a relaxation time could be derived from static shear viscosity over a wide temperature range, for the well-known glass forming substance ${\mathrm{Ca}}_2$ ${\mathrm{K}}_3$(${\mathrm{NO}}_3$ ${)}_7$. The calculated relaxation time compares favorably with relaxation times obtained by other methods. This agreement supports the validity of a simple SED model over a wide frequency range.